Whether an affliction of the diaphragm disturbs the intellect.

One inquires further whether an affliction of the diaphragm disturbs the intellect.

It seems not. For the intellect is not subject to harm and is incorruptible, according to Aristotle in the third book of On the Soul. Therefore, it is not moved or disturbed by an affliction in the diaphragm.

In addition, the incorporeal is not affected by the corporeal. But the intellect is incorporeal and does not use a bodily organ. Therefore, it cannot be affected by the diaphragm.

The Philosopher says the opposite.

One must reply that an affliction in the diaphragm does move and disturb the intellect per accidens, but not per se. And the reason for this is that the diaphragm is an abundantly nerve-filled web and particularly sensitive. As a result, it shares in the nature of the webs of the brain, and because it is near the heart and is a sort of medium through which the heart infuses its powers into other members, this is why, when the diaphragm is blocked, of necessity the heart's influence is withdrawn from the other parts.

Further, although the intellect is not an organic power, nevertheless it needs other powers which do use organs, since nothing can be understood without a phantasm, as is said in book three of On the Soul, because the intellect either is a phantasm or does not exist without a phantasm. And this is just what happens when the intellect's operation is impeded by an injury to the power of memory or phantasms, as is evident among the insane or those suffering lethargy [lytargici ], not because the intellect uses some organ but because it abstracts species from sensibles and strips and despoils them of matter. Thus the intellect is disturbed by an injury to the diaphragm, because, once an injury has occurred, the heart too is damaged and the influences of the heart are withdrawn from the other members.

With this, one can respond to the arguments. For they prove that an affliction in the diaphragm does not disturb the intellect per se, but just as has been said.

Whether touching the diaphragm is a cause of laughter.

One inquires further whether touching the diaphragm is a cause of laughter.

1. It seems not, because one and the same thing is not the cause of contraries. But it has already been said that touching the diaphragm is a cause of pain, and therefore it cannot be a cause of laughter.

2. In addition, laughter arises from the purity of the blood and the thinness of the spirits. But these do not arise from the diaphragm, and therefore, etc.

The Philosopher says the opposite.

One must reply that the movement of the diaphragm is a cause of laughter. And the reason for this is that laughter arises from a perception of something agreeable and pleasant, just as, in a contrary fashion, weeping arises from the apprehension of something disagreeable. Now, however, when something touches the diaphragm or some part near it without causing it damage, a certain warming and a certain tickle is caused by this motion in the diaphragm, and from its warming the blood in the arteries of the heart is thinned, and the cleaner the blood is the more agreeable it is to nature. This is why laughter arises from the warming of the diaphragm, because the mouth and the face are indicators of interior dispositions.

Something that contributes a great deal to this is the fact that whatever is very sensitive easily apprehends a contrary thing and, as a result, is easily oppressed by pain. Similarly, that same thing, because it is particularly sensitive, is easily subject to pleasure when it apprehends something agreeable. And the diaphragm is very sensitive, and heat is agreeable to nature, and this is why pleasure proceeds from the warming of the diaphragm.

1. By this a response is evident to the argument, that one and the same thing is not a cause of contraries in one and the same way, but nevertheless can be a cause of contraries in diverse ways.

2. A response has already been stated to the second argument, and so much for it. Therefore, according to some, when the diaphragm is touched by the heart, it sounds like a drum [tympanum]. In this way the sound of laughter is caused, etc.